Liquid transfer systems have been and will remain an important aspect of municipal services and commercial facilities management. The protection of ground water and natural bodies of water requires systems for diverting and/or treating water that contacts roadways, parking lots, and other man made structures. If such diversion or treatment systems are not provided, particulate and contaminants located on or forming part of such structures may be carried by drain water or stormwater to natural water bodies and contaminate them. Local, state and federal laws and rules require municipalities, businesses and, in some instances, private entities, to establish means to reduce particulate and contaminant levels permissibly transferred to natural bodies of water from property under their control. Particular requirements may vary from jurisdiction to jurisdiction, but all are likely to become more, rather than less, stringent.
Previously, municipal water transfer and treatment facilities provided the only mechanism for diverting contaminated water away from natural bodies of water, either for holding or treatment for subsequent transfer to natural settings. In general, that process involved, and continues to involve, the establishment of a system of drains, such as in a parking lot or at a street curb, by which water enters a system of pipe conduits. Eventually, the water received from the drains reaches either a final outlet destination or is directed to a treatment system for contaminant removal. For purposes of this application, “contaminated water” is to be understood to mean any water including floating particulate, such as closed-cell extruded polystyrene foam and oil, for example; non-floating particulate, such as sand and silt, for example; and entrained contaminants, such as dissolved nutrients or metals, for example. All of these undesired materials will be, in most instances, referred to herein generally as contaminants. As used herein the term “particulate” is to be understood to include floating particulate and/or non-floating particulate.
Land development produces increased levels of drain water and stormwater runoff, resulting in increased strain on existing water transfer and treatment infrastructure and an increased likelihood of natural water contamination. In an effort to reduce the impact of development on natural resources and municipal services, initial upstream treatment has become a requirement in many land development, restoration and repair projects. That is, requirements in various forms have been established to ensure that before contaminated water enters the municipal water transfer and/or treatment system or natural receiving waters, it must be treated in a manner that reduces the level of contaminants entering the municipal system or natural receiving waters. Therefore, most new land development plans and upgrades to existing paved surfaces involve the insertion of a preliminary separation system, generally for connection to the municipal water-handling infrastructure.
Any preliminary separation system should be designed with the capability to receive liquid flowing in at a wide range of rates. For example, a mild rainfall resulting in rain accumulation of less than 0.25 inches over a span of 24 hours produces a relatively low flow rate through the system. On the other hand, for example, a torrential rainfall resulting in rain accumulation of more than two inches over a span of three hours produces relatively high flow rates through the system. It is desirable, then, to have a separation system capable of handling variable flow rates with reduced likelihood of backup and flooding of the surface above. It is also desirable to control the flow through the system such that scouring or wash out of previously trapped particulates during high flows is reduced.
A variety of stormwater separation systems exist. These systems may be characterized generally as a tank or container including a storage or treatment chamber within which, ideally, floating particulates are retained, and non-floating particulates are allowed to settle. The storage chamber includes an inlet for receiving untreated water, and an outlet for movement of treated water out of the chamber. The tank may also include a bypass arrangement to allow excess untreated water to exit the tank without passing through the storage chamber. In many cases, the storage chamber is arranged with the inlet and outlet located at the chamber perimeter. Often, the inlet and outlet are spaced away from each other, but in some cases may be arranged near each other.
Advancements in manufacturability, cost and effectiveness of separation systems continue to be sought.